Spectrum analyzer

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Spectrum analyzer

Spectrum Sweep screen

Press F + 5 NOAA to turn on the Spectrum analyzer. The current VFO or memory frequency will be the center frequency of the spectrum sweep.

The spectrum analyzer can also be used with ScnRng mode.

Note

• PTT opens detail monitoring for the last received frequency
• with ScnRng, the blacklist is limited to 15 frequencies

Important

The spectrum analyzer does not behave identically across radio hardware. The V1 / V2 radios are built around the BK4819 receiver, while the V3 (K5v3) uses the BK4829. These are different receiver chips, with a different front-end, LNA/PGA gain stages, AGC behaviour and RSSI scaling.

As a result:

• the noise floor, the absolute dBm / S-meter readings and the LNAs / LNA / PGA values are not directly comparable between a V1/V2 and a V3 — a level or gain setting that looks "right" on a V2 has no reason to mean the same thing on a V3;
• the spectrum analyzer was substantially reworked to support both platforms, so do not expect a V3 to reproduce, value for value, what you observed on an older V1/V2;
• a high or unstable noise floor is largely driven by the receiver front-end and the local RF environment, not by a bug in the analyzer. When AUTO cannot settle on your local floor, switch to MANUAL and set the trigger yourself — that is exactly what MANUAL mode is for.

Trigger modes: AUTO vs MANUAL

Short-press M to toggle between AUTO and MANUAL trigger modes. The top-left indicator shows the active mode:

• A:NORM / A:WEAK / A:STRG — AUTO mode. The squelch trigger level tracks the measured noise floor using a sensitivity profile:

  • WEAK — +12 dB above noise floor (least sensitive, fewer false openings)
  • NORM — +8 dB (default)
  • STRG — +5 dB (most sensitive)

  A direction arrow is appended to the label to show the current sweep direction:

  • > — sweep going left → right
  • < — sweep going right → left

  Example: A:NORM> means AUTO / Normal sensitivity, sweeping to the right.

• M <rssi>/<trig> — MANUAL mode. You set the squelch trigger level yourself with * / F, and the vertical scale (dbMax) with 3 / 9. The trigger changes in predictable 1 dB steps.

Long-press M to reset the spectrum analyzer to its default settings.

Saving settings on exit

When you leave the Spectrum Sweep screen with EXIT, the spectrum analyzer writes its persistent settings to flash. The next time you open the analyzer, these values are restored:

• frequency step between bars (1 / 7)
• number of bars / channels (4)
• receiver bandwidth used while monitoring a signal (6)
• trigger mode, AUTO or MANUAL (M short)
• AUTO sensitivity profile, WEAK / NORM / STRG (3 / 9 in AUTO mode)
• squelch trigger level (* / F) — restored in MANUAL mode; in AUTO the trigger is recomputed from the noise floor each time you open the analyzer

This persistence was expanded after v5.4.0: older builds saved only the scan step, bar count, and receiver bandwidth. In current builds, starting the spectrum analyzer from ScnRng mode no longer overwrites the saved scan step or bar-count preference; the active scan range still defines the sweep span.

The vertical scale (dbMax, 3 / 9 in MANUAL) is not persisted: it is reset to the default display window every time the analyzer is opened. The current sweep frequency/window, the UP / DOWN scrolling step, modulation type, backlight toggle, temporary blacklist, and detail-monitor register adjustments (LNAs, LNA, PGA) are also not saved by this EXIT action. If you are on the Detail Monitor screen, EXIT first returns to the sweep screen; press EXIT again from there to save and leave the analyzer.

Current builds also improve 8.33 kHz frequency rounding in bandscope / spectrum workflows, so displayed and tuned frequencies stay aligned more predictably on aviation-style steps.

Button functions

Key	Function
1 / 7	Increase / decrease frequency step between bars
2 / 8	Increase / decrease the frequency step used when scrolling with UP / DOWN
3 / 9	In MANUAL: adjust dbMax (vertical scale) · In AUTO: cycle sensitivity profile (WEAK ↔ NORM ↔ STRG)
4	Toggle the number of bars (channels) in the graph
5	Frequency input for the lower sweep frequency (value in MHz, * = decimal point)
6	Toggle receiver bandwidth
0	Toggle modulation type (FM / AM / USB)
* / F	Increase / decrease squelch trigger level in 1 dB steps — takes effect in MANUAL; in AUTO the auto-tracker overrides it on the next sweep
M short	Toggle AUTO / MANUAL trigger mode
M long	Reset spectrum analyzer to defaults
UP / DOWN	Shift the sweep window up / down in frequency · During RX: stop reception and resume the sweep in the chosen direction
Side button 1️⃣	Exclude the current frequency from the spectrum scan
Side button 2️⃣	Toggle backlight
PTT	Switch to detail monitoring of the last received frequency
EXIT	Save persistent spectrum settings, then return to the previous screen / function

Tip

The sweep alternates direction on each full cycle to reduce directional bias. The < / > indicator next to A:xxxx lets you see at a glance which half of the sweep is currently active.

Note

In MANUAL mode, the spectrum curve is drawn without cosmetic smoothing. This makes narrow peaks line up more closely with the raw RSSI used by the squelch detector.

Detail Monitor screen

Button functions

• M - scrolls through the parameters displayed at the bottom of the screen, which can be adjusted with the UP and DOWN buttons
  • LNAs - Short Low Noise Amplifier
  • LNA - Low Noise Amplifier
  • PGA - Programmable Gain Amplifier
• Side button 1️⃣ - toggle monitor mode (forces the squelch open so you can hear the tuned frequency continuously)
• EXIT - exits to the previous screen of the spectrum analyzer

Note

LNAs / LNA / PGA are live diagnostic values, not saved settings. They are driven by the receiver's AGC and are not persisted on exit. Their available steps and their meaning differ between the BK4819 (V1/V2) and the BK4829 (V3), so they cannot be compared value for value across platforms.

Related pages

• Getting started
• Scanning
• Button functions
• Radio operation
• Troubleshooting